Nanoparticle Networks Research Articles

Colloidal processing of low-concentrated zirconia nanosuspension using osmotic consolidation

Colloidal processing was applied to a water-based suspension with 5vol% zirconia nanoparticles of 10–15nm in size. The nanosuspension was concentrated by evaporation or by a newly developed method of osmotic dehydration. The viscosity and stability of concentrated nanosuspensions were investigated. Osmotic consolidation of both nanosuspensions, concentrated by evaporation and osmotically dehydrated, was performed in a solution of polyethylene oxide separated from the nanosuspensions using a permeable membrane. Osmotic pressure generated a water flow from the nanosuspension to the polymer solution, concentrating the nanosuspension and eventually consolidating the nanoparticle network. The pore size distribution in dried nanoparticle compacts and pore size evolution during sintering were evaluated and discussed. The nanozirconia compacts were densified by pressure-less sintering to a relative density of up to 99.7% while maintaining the nanocrystalline structure.

Ultra-Porous Nanoparticle Networks: A Biomimetic Coating Morphology for Enhanced Cellular Response and Infiltration.

Orthopedic treatments are amongst the most common cause of surgery and are responsible for a large share of global healthcare expenditures. Engineering materials that can hasten bone integration will improve the quality of life of millions of patients per year and reduce associated medical costs. Here, we present a novel hierarchical biomimetic coating that mimics the inorganic constituent of mammalian bones with the aim of improving osseointegration of metallic implants. We exploit the thermally-driven self-organization of metastable core-shell nanoparticles during their aerosol self-assembly to rapidly fabricate robust, ultra-porous nanoparticle networks (UNN) of crystalline hydroxyapatite (HAp). Comparative analysis of the response of osteoblast cells to the ultra-porous nanostructured HAp surfaces and to the spin coated HAp surfaces revealed superior osseointegrative properties of the UNN coatings with significant cell and filopodia infiltration. This flexible synthesis approach for the engineering of UNN HAp coatings on titanium implants provides a platform technology to study the bone-implant interface for improved osseointegration and osteoconduction.

(Invited) Understanding Cathodes for Solid Acid Fuel Cells By Coupling FIB-SEM 3D Reconstruction with Mathematical Modeling

Fuel cells based on the crystalline proton-conducting electrolyte CsH2PO4 (CDP) typically operate between 230 °C and 260 °C1. In this intermediate temperature regime, so-called solid acid fuel cell (SAFC) anodes are tolerant to high concentrations of impurities2, are amenable to internal reforming of multiple fuels3, and may possibly omit platinum entirely4. These properties make SAFCs excellent candidates for stationary fuel cell systems operating on fuels such as methanol or natural gas. A longstanding barrier to the adoption of SAFC technology has been the low activity and high precious metal content of the cathode. In the state-of-the-art cathode architecture, a macroporous framework of the CDP electrolyte is decorated with a percolating network of platinum nanoparticles that acts as both the oxygen reduction catalyst and the sole electronic conductor in the electrode. Typical SAFC cathode Pt loadings are greater than 1.75 mg/cm2, an amount circumscribed by the minimum quantity needed to obtain sufficient electrical conductivity in the electrode5. Despite the success of the current SAFC cathode design, only limited work has been done to date to understand the structure-property relationships governing its performance. Here we address this problem using an approach coupling ex situmicroscopic characterization and mathematical modeling with experimental input from electrochemical cell testing. Porous SAFC cathodes were sectioned using FIB/SEM to render a 3D reconstruction of a representative electrode sub-volume. A machine-learning algorithm was used to automatically segment image stacks to address segmentation problems due to gray level gradients and overlapping gray level peaks in the image histogram. Numerical analysis was performed to extract electrode physical properties (i.e. porosity, tortuosity). Electrode physical parameters from the 3D electrode reconstruction were used as inputs to a 1D macrohomogenous model similar to those applied previously to PEM fuel cells6. The model was used to self-consistently fit SAFC polarization curves, yielding, among other quantities, an electrochemically active area for the electrode, which has been notoriously difficult to measure in the SAFC system. We comment on these and other findings, as well as the utility of the model in addressing the SAFC system given some of the categorical distinctions between it and the PEM system. Acknowledgments This work is supported by ARPA-E via cooperative agreement DE-AR0000499. References 1 S.M. Haile, C.R.I. Chisholm, Kenji Sasaki, D.A. Boysen, and T. Uda, Faraday Discuss. 134, 17 (2007). 2 C. R. I. Chisholm, Dane A. Boysen, A. B. Papandrew, Strahinja K Zecevic, Sukyal Cha, Kenji A Sasaki, Áron Varga, Konstantinos P. Giapis, and S.M. Haile, Electrochem. Soc. Interface 18, 53–59 (2009). 3 T. Uda, D.A. Boysen, C. R. I. Chisholm, and S.M. Haile, Electrochem. Solid-State Lett. 9, A261 (2006). 4 Alexander B. Papandrew, Robert W. Atkinson III, Raymond R. Unocic, and Thomas a. Zawodzinski, J. Mater. Chem. A 3, 3984–3987 (2015). 5 Alexander B. Papandrew, Calum R.I. Chisholm, Ramez A Elgammal, Mustafa M. Özer, and Strahinja K Zecevic, Chem. Mater. 23, 1659–1667 (2011). 6 T.E. Springer, T.A. Zawodzinski, and S Gottesfeld, J. Electrochem. Soc. 138, 2334 (1991).

Stability of ZnO/Self-Assembled Gold Nanoparticle Network Film

Stability of ZnO/Self-Assembled Gold Nanoparticle Network Film

The influence of architecture of nanoparticle networks on collective charge transport revealed by the fractal time series and topology of phase space manifolds

The influence of architecture of nanoparticle networks on collective charge transport revealed by the fractal time series and topology of phase space manifolds

Label-free DNA biosensor based on resistance change of platinum nanoparticles assemblies

A novel nanoparticle based biosensor for the fast and simple detection of DNA hybridization events is presented. The sensor utilizes hybridized DNA's charge transport properties, combining them with metallic nanoparticle networks that act as nano-gapped electrodes. The DNA hybridization events can be detected by a significant reduction in the sensor's resistance due to the conductive bridging offered by hybridized DNA. By modifying the nanoparticle surface coverage, which can be controlled experimentally being a function of deposition time, and the structural properties of the electrodes, an optimized biosensor for the in situ detection of DNA hybridization events is ultimately fabricated. The fabricated biosensor exhibits a wide response range, covering four orders of magnitude, a limit of detection of 1nM and can detect a single base pair mismatch between probe and complementary DNA.

Tuning the Mechanical Properties of Polymer-Grafted Nanoparticle Networks through the Use of Biomimetic Catch Bonds

The ability to precisely tune the mechanical properties of polymeric composites is vital for harnessing these materials in a range of diverse applications. Polymer-grafted nanoparticles (PGNs) that are cross-linked into a network offer distinct opportunities for tailoring the strength and toughness of the material. Within these materials, the free ends of the grafted chains form bonds with the neighboring chains, and tailoring the nature of these bonds could provide a route to tailoring the macroscopic behavior of the composite. Using computational modeling, we simulate the behavior of three-dimensional PGN networks that encompass both high-strength “permanent” bonds and weaker, more reactive labile bonds. The labile connections are formed from slip bonds and biomimetic “catch” bonds. Unlike conventional slip bonds, the lifetime of the catch bonds can increase with an applied force, and hence, these bonds become stronger under deformation. With our 3D model, we examined the mechanical response of the comp...

Rapid synthesis of inherently robust and stable superhydrophobic carbon soot coatings

The fabrication of superhydrophobic coatings using a candle flame or rapeseed oil has become very attractive as a novel approach for synthesis of water repellent surfaces. Here, we report an improved, simplified and time-efficient method for the preparation of robust superhydrophobic carbon soot that does not require any additional stabilizers or chemical treatment. The soot's inherent stabilization is achieved using a specially-designed cone-shaped aluminum chimney, mounted over an ignited paper-based wick immersed in a rapeseed oil. Such configuration decreases the level of oxygen during the process of combustion; altering the ratio of chemical bonds in the soot. As a result, the fractal-like network of the carbon nanoparticles is converted into dense and fused carbon chains, rigidly coupled to the substrate surface. The modified carbon coating shows thermal sustainability and retains superhydrophobicity up to ∼300°C. Furthermore, it demonstrates a low contact angle hysteresis of 0.7–1.2° accompanied by enhanced surface adhesion and mechanical durability under random water flows. In addition, the soot's deposition rate of ∼1.5μm/s reduces the exposure time of the substrate to heat and consequently minimizes the thermal effects, allowing the creation of superhydrophobic coatings on materials with low thermal stability (e.g. wood or polyethylene).

Structural studies on drop-cast film based on functionalized gold nanoparticles network: The effect of thermal treatment

In the present work the role of the thermal treatment on the reorganization of gold nanoparticles (AuNPs) functionalized with a π-conjugated dithiol ligand, namely 9,9-didodecyl-2,7-bis-thiofluorene, is studied by grazing incidence X-ray diffraction technique. For a detailed investigation of the structural changes and reorganization occurring in the AuNPs network and of the monitoring of complex interactions between nanoparticles, the line profiles are analyzed in out-of-plane and in-plane directions. The obtained data support the idea of the formation of a uniform network of nanoparticles that after annealing are extended from hexagonal to cubic arrangement.

Two-dimensional percolation threshold in confined Si nanoparticle networks

Non-percolating and percolating silicon quantum dot (QD) networks were investigated by plane-view energy filtered transmission electron microscopy (EF-TEM). The Si QD networks were prepared by plasma enhanced chemical vapor deposition on free standing 5 nm Si3N4 membranes, followed by high temperature annealing. The percolation threshold from non-percolating to percolating networks is found to be in between a SiOx stoichiometry of SiO0.5 up to SiO0.7. Using the EF-TEM images, key structural parameters of the Si QD ensemble were extracted and compared, i.e., their size distribution, nearest neighbor distance, and circularity. Increasing the silicon excess within the SiOx layer results in an ensemble of closer spaced, less size-controlled, and less circular Si QDs that give rise to coupling effects. Furthermore, the influence of the structural parameters on the optical and electrical Si QD ensemble properties is discussed.

DNA–gold nanoparticles network based electrochemical biosensors for DNA MTase activity

In this work, a highly sensitive electrochemical DNA methyltransferase (MTase) activity assay was fabricated with DNA–gold nanoparticles (Au NPs) network as signal amplification unit and an easy assembly method by the linkage of benzenedithiol bridge. By two complementary AuNPs modified single-stranded DNA, DNA–gold nanoparticles network was self-assembled. With the linkage of benzenedithiol bridge, the DNA network structure was immobilized on the surface of gold electrode through the covalent Au–S bond. In the presence of Dam MTase, the special sites of DNA–AuNPs network were methylated and could not be digested by restriction endonuclease Mbo I. Thus the loaded electrochemical indicator Methylene blue (MB) was MB molecules still remained on the DNA–Au NPs network. The electrochemical response depended on the methylated degree, which could be used to detect MTase activity. By the differential pulse voltammetry (DPV), it was demonstrated that a linear relationship between the DPV response and logarithm of Dam concentration ranged from 0.075 to 30U/mL, achieving a low detection limit of 0.02U/mL. The use of benzenedithiol avoided the direct incubation of the solid electrode with the capture DNA probe under complex and harsh conditions. Therefore the immobilization of DNA–AuNPs network was easy to be carried out, which is favorable for the specially high stability and reproducibility of the electrochemical biosensor.

Enhanced electrical conductivity in graphene-filled polycarbonate nanocomposites by microcellular foaming with sc-CO2

Electrically conductive polycarbonate (PC) foams containing a low concentration of graphene nanoplatelets (0.5 wt.%) were produced with variable range of expansion ratio by applying a high-pressure batch foaming process using sc-CO2. The structure of the foams was assessed by means of SEM, AFM and WAXS, and the electrical conductivity was measured in the foam growing direction. Results showed that electrical conductivity of PC composite foams remarkably increased when compared to that of non-foamed PC composite, with both the electrical conductivity and the main cell size of the foams being directly affected by the resultant expansion ratio of the foam. This interesting result could be explained by the development of an interconnected graphene nanoparticle network composed by increasingly well-dispersed and reoriented graphene nanoplatelets, which was developed into the solid fraction of the foam upon foaming by sudden depressurising of the plasticised CO2-saturated PC preform. Some evidences of morphological changes in the graphene nanoplatelets after foaming were obtained by analysing variations in graphene’s (0 0 2) diffraction plane, whose intensity decreased with foaming. A reduction of the average number of layers in the graphene nanoplatelets was also measured, both evidences indicating that improved dispersion of graphene nanoparticles existed in the PC composite foams. As a result, foams with a proper combination of low density and enhanced electrical conductivity could be produced, enabling them to be used in applications such as electromagnetic interference shielding.

Stereoregular High-Density Bottlebrush Polymer and Its Organic Nanocrystal Stereocomplex through Triple-Helix Formation

We report the synthesis of a well-defined molecular bottlebrush polymer with stereoregular side chains (i.e., syndiotactic PMMA). The simultaneous control over the molecular weight, side-chain tacticity, and architecture allows the macromolecule to stereocomplex with the complementary linear stereoregular polymers (i.e., isotactic PMMAs) in controlled manners. By modulating the feed ratio of the complexing materials and chain length of the linear assembling component, a variety of crystalline materials with different sizes and morphologies, including discrete spherical nanoparticle, multiple-particle assembly, and cross-linked network structure, can be produced. Among these, uniformed sized, stable nanocrystals that exhibit temperature-induced solution assembly and disassembly properties can be derived from a combined process of PMMA triple-helix stereocomplex formation and polymer architecture-directed intramolecular crystallization. This work has established a new, facile synthetic protocol toward stimuli-responsive organic nanocrystals, which is applicable to the fabrication of a wide variety of functional crystal nanomaterials with practical applications.

Characteristics of DNA-AuNP networks on cell membranes and real-time movies for viral infection.

This data article provides complementary data for the article entitled “DNA-AuNP networks on cell membranes as a protective barrier to inhibit viral attachment, entry and budding” Li et al. (2016) [1]. The experimental methods for the preparation and characterization of DNA-conjugated nanoparticle networks on cell membranes were described. Confocal fluorescence images, agarose gel electrophoresis images and hydrodynamic diameter of DNA-conjugated gold nanoparticle (DNA-AuNP) networks were presented. In addition, we have prepared QDs-labeled RSV (QDs-RSV) to real-time monitor the RSV infection on HEp-2 cells in the absence and presence of DNA-AuNP networks. Finally, the cell viability of HEp-2 cells coated by six types of DNA-nanoparticle networks was determined after RSV infection.

Free-Standing Monolayered Metallic Nanoparticle Networks as Building Blocks for Plasmonic Nanoelectronic Junctions.

The effective coupling of optical surface plasmons (SPs) and electron transport in a plasmonic-electronic device is one of the fundamental issues in nanoelectronics and the emerging field of plasmonics, and offer promise in providing a solution to next generation nanocircuits in which all coupling is in the near field. Attempts toward this end, however, are limited because of the integration challenge to compatible nanodevices. To date, direct electrical detection of SP-electron coupling from metallic nanostructures alone are not reported, and thus it remains a great experimental challenge. In this paper, we succeed in preparing a new suspended-film-type nanoelectronic junction, in which free-standing 2D fractal nanoparticle networks act as plasmonically active nanocomponents. Direct electrical detection of optical collective SPs was evidenced by photocurrent response of the junction upon illumination. Room-temperature I-V characteristics, differing from nonlinear to Ohmic behaviors, are found to be sensitive to the nanometer-scale morphology changes of the nanomembranes. The finding and approach may enable the development of advanced plasmonic nanocircuits and new nanoelectronics, nanophotonics, and (solar) energy applications.

Formation of nanoparticle added functional polymer network membrane via micro-phase separation process

Electro-conductive membranes formed by carbon nanoparticle network array were fabricated via micro-phase separation process in the polymer system of cellulose acetate/acetone/water ternary solution. Micro-phase separation technique is the most common method for preparation and production of polymeric membrane. With the formation of polymer network, added nanoparticles became network by the drive of non-solvent owing to thermodynamic and compatible properties between particles and ternary solution. Meanwhile, the nanoparticle surface properties affected the binding force of neighbor particles for the continuous nanoparticle network structure. Heat treatment on the membrane aims at removing polymer from. Thus, electro-conductive nanoparticle network membrane can be facilely prepared.

Fabrication of Pd/P nanoparticle networks with high activity for methanol oxidation

The as-prepared Pd/P nanoparticle networks efficiently exhibit electrocatalytic activity and stability for methanol oxidation.

Unprotected and interconnected Ru0 nano-chain networks: advantages of unprotected surfaces in catalysis and electrocatalysis.

Seedless, surfactantless and support-free unprotected, metallic, interconnected nano-chain networks of ruthenium nanoparticles (NPs) were successfully synthesized via the reduction of ruthenium(iii) chloride (RuCl3) with sodium borohydride (NaBH4) at three different temperatures, viz. 30 °C, 45 °C and 60 °C. The molar ratio of RuCl3 solution and borohydride was optimized to be 1 : 1.5 to produce stable colloids with the optimum final solution pH of 9.7 ± 0.2. Average diameters of the interconnected nano-chain networks prepared at 30 °C (Ru-30), 45 °C (Ru-45) and 60 °C (Ru-60) were 3.5 ± 0.5 nm, 3.0 ± 0.2 nm and 2.6 ± 0.2 nm respectively. The morphology and composition dependent catalytic and electrocatalytic activities of these unprotected Ru nano-chain networks (Ru-30, Ru-45 and Ru-60) were studied in detail. The catalysis study was performed by investigating the transfer hydrogenation of several substituted aromatic nitro compounds. It was observed that Ru-60 was relatively more active compared to Ru-30 and Ru-45, which was reflected in their rate constant values. The electrocatalytic activities of Ru-30, Ru-45 and Ru-60 were screened for anodic water splitting in alkaline medium (0.1 M NaOH) and it was found that all of them showed almost the same activity which required an over-voltage of 308 ± 2 mV to obtain an anodic current density of 10 mA cm-2. The catalytic and electrocatalytic performances of these unprotected Ru0 networks were compared with Ru0 nanomaterials prepared under similar conditions with three different surfactants, viz. CTAB, SDS and TX-100, which revealed that unprotected Ru0 networks are better catalysts than those stabilized with surfactants. The superior catalytic and electrocatalytic performance is due to the availability of unprotected Ru0 surfaces. The present route may provide a new possibility of synthesizing other surfactant-free, unprotected metal colloids for enhanced catalytic and electrocatalytic applications.

An enzyme-free catalytic DNA circuit for amplified detection of aflatoxin B1 using gold nanoparticles as colorimetric indicators.

An enzyme-free biosensor for the amplified detection of aflatoxin B1 has been constructed based on a catalytic DNA circuit. Three biotinylated hairpin DNA probes (H1, H2, and H3) were designed as the assembly components to construct the sensing system (triplex H1-H2-H3 product). Cascaded signal amplification capability was obtained through toehold-mediated strand displacement reactions to open the hairpins and recycle the trigger DNA. By the use of streptavidin-functionalized gold nanoparticles as the signal indicators, the colorimetric readout can be observed by the naked eye. In the presence of a target, the individual nanoparticles (red) aggregate into a cross-linked network of nanoparticles (blue) via biotin-streptavidin coupling. The colorimetric assay is ultrasensitive, enabling the visual detection of trace levels of aflatoxin B1 (AFB1) as low as 10 pM without instrumentation. The calculated limit of detection (LOD) is 2 pM in terms of 3 times standard deviation over the blank response. The sensor is robust and works even when challenged with complex sample matrices such as rice samples. Our sensing platform is simple and convenient in operation, requiring only the mixing of several solutions at room temperature to achieve visible and intuitive results, and holds great promise for the point-of-use monitoring of AFB1 in environmental and food samples.

Ultraporous superhydrophobic gas-permeable nano-layers by scalable solvent-free one-step self-assembly.

Superhydrophobic materials with excellent humidity tolerance, high porosity and light transmittance are being investigated for numerous applications including moisture-sensitive catalysts and perovskite solar cells. Here, we report the one-step solvent-free synthesis of ultraporous superhydrophobic nano-layers by the on-the-fly functionalization of nanoparticle aerosols. Short exposure of surfaces to hot Mn3O4, ZnO and TiO2 aerosols results in ultraporous nanoparticle networks with repulsive dewetting state approaching ideal Cassie-Baxter superhydrophobicity. In addition to showcasing sliding angles of ca. 0° and very low contact angle hysteresis of 3° ± 2°, these optimal nano-layers have up to 98% porosity and pore size of several micrometres, a key feature to enable efficient penetration of gases to the substrate surface. The stability of this ultraporous superhydrophobic morphology is demonstrated by rapidly applying Moses effect-functionality to substrates that parts water up to 5 mm high. This scalable synthesis method offers a flexible and rapid approach for the production of numerous moisture-resistant devices including gas sensors, catalysts and perovskite solar cells.